The present invention relates to a multiplexed data memory system in which an external memory control unit which receives a write command from a host unit and which memorizes the received write command in an external memory unit under its control as original data writes the same data as that original data in the external memory unit operable under different external memory control units as backup data. More particularly, the present invention relates to a multiplexed data reorganizing system capable of effectively utilizing backup data and which is also able to efficiently reorganize the duplexing of original data obtained after backup data was used and the backup data, and relates to a subsystem for carrying out this system.
In a multiplexed data memory system in which data used in a host unit such as a host computer is multiplexed and held by a plurality of external memory units, e.g. original external memory unit and sub-external memory unit, as a method of holding the multiplexing of data between the original external memory unit and the sub-external memory unit, there are generally known technologies disclosed in Japanese Published Unexamined Patent Application No. Hei 6-214853, Japanese Published Unexamined Patent Application No. Hei 7-6099, Japanese Patent No. 2509460 and Japanese Translation of PCT Application No. Hei 8-509565. According to the method disclosed in the above-mentioned technologies, an original external memory unit and sub-external memory unit are provided under control of different external memory control units, the original external memory control unit and the sub-external memory control unit are connected via an interface cable and a write command received at the original-side external memory control unit is issued to the sub-side external memory control unit, thereby resulting in the multiplexing of data of the original external memory unit and the sub-external memory unit being maintained.
In such multiplexed data memory system, as a method of reorganizing the multiplexing after the multiplexing is interrupted, there is known a method of copying only an update place of an original external memory unit which is interrupted in multiplexing to a sub-side external memory unit, i.e. so-called difference copy.
In this difference copy, data of the sub-side external memory unit is generally used as backup data of the original-side external memory unit. During data is duplexed, a write access and a read access are generally inhibited from a standpoint of coincidence of original data and sub-data.
Recently, although a demand of effectively utilizing backup data increases from a standpoint of increasing an efficiency of a business, an inefficient procedure should be unavoidably made in order to reorganize the multiplexing after the access on the backup data was ended.
When backup data is temporarily used as test program data by utilizing the duplexed data memory system, for example, or when backup data of data of a certain time point is obtained from a sub-side external memory unit and saved in other memory medium, further when a trouble occurs the sub-side external memory unit and when the sub-side external memory unit is accessed in order to execute a program for restoring such trouble, if the duplexing of data should be released and the duplexing of data should be formed again, then all data of the original-side external memory unit should be copied to the sub-side external memory unit.
However, in this case, when a difference of several tracks at most occurs in the original-side and sub-side data due to the access on the sub-side external memory unit, according to the above-mentioned method of reorganizing the multiplexed data, there is then the problem that an efficiency of re-arrangement is not excellent.
Also, when a business is temporarily shifted to the sub-side system, the duplexed state of data should be released. When the business is again returned to the original-side system, the old sub-side system is provisionally set in the original-side system and the old original-side system is provisionally set in the sub-side system thereby duplexing the data. Further, the duplexed state is released, the provisional sub-side system is returned to the original system, the provisional original-side system is returned to the subsystem and the business is resumed in the inherent original-side system. Such a complex procedure should be executed.
That is, in the conventional multiplexed data memory system, the multiplexed state should be released in order to access the backup data. When the multiplexing is reorganized after the accessing was ended, an inefficient procedure requiring the initialization should be executed.
A problem of the present invention is that, under circumstances in which the multiplexing of data is organized, after read and write accessing was made on data generally saved as backup data, the multiplexing of data may be reorganized efficiently.
A fundamental feature of the present invention lies in that, under circumstances in which the multiplexing of data is organized, after read and write accessing was made on data generally saved as backup data, when the multiplexing of data is organized again, the multiplexing may be reorganized efficiently by copying only the update places obtained by the access from the original system to the subsystem or from the subsystem to the original system.
A feature of the multiplexed data processing system according to the present invention has a function to issue an original disk control unit write command to the sub-disk control unit which controls the backup data in the multiplexed data memory system in which disk units which are under control of different disk control units have the same data.
Thus, update places of original and sub data updated during data is multiplexed are registered on the access information management table of the original disk control unit as access information. When the original disk control unit receives a duplexing resume command, it becomes possible to efficiently reorganize the duplexing by copying original data corresponding to the access place occurred in the duplexing interruption from the information of the access information management table to the backup data or copying the backup data to the original data.
Also, a feature of the multiplexed data processing system according to the present invention is that it has a function to register access places on the access information management table.
The duplexing re-arrangement in the duplexed data memory system according to the present invention and its action will be described concretely as follows.
Initially, each time the write access occurs in the backup data obtained during the duplexing is interrupted in the channel command analyzing section of the subsystem, the access place is registered on the access information management table.
Then, when the channel command analyzing section receives an access end command relative to the backup data, the channel command analyzing section reports it to the original system. The original system reads out information from the access information management table of the subsystem, merges the read-out information to the access information of the original system and registers the merged information on the access information management table.
When the channel command analyzing section of the original system receives the duplexing resume command, the access information management table is checked, and a write command or a read command of data of the access place is issued to the subsystem, thereby reorganizing the duplexing.
The feature of the present invention will be described more in detail. The present invention is a subsystem comprising means for recognizing whether or not the access of the original side external memory control unit on the sub-side external memory unit is started or ended and means for judging which data of the original-side and sub-side external memory control units should be used as original data when the duplexing of data is reorganized after the backup data was updated and wherein the original-side and sub-side external memory control units include means for recognizing the access situation of the backup data.